In order to fabricate a lens, in particular an ophthalmic lens, it is conventional to form a transparent substrate by molding, thermoforming, and/or machining a synthetic resin or a mineral glass, and subsequently to deposit one or more coating layers imparting various optical or mechanical properties to the lens such as an ability to withstand impacts or abrasion, attenuating reflections, photochromy, etc. Thus, typically, the following are deposited in succession on at least one of the faces of an ophthalmic lens: a so-called primer layer; a hard layer providing resistance to abrasion; and finally an optional anti-reflection layer. The primer layer favors bonding of the hard layer and generally reinforces impact resistance. Primer layers and hard layers are generally constituted by varnish.
In industrial processes for fabricating lenses, and in particular ophthalmic lenses, these varnish layers are deposited by centrifuging or dipping in a bath of solution or by dispersing the varnish on the corresponding face of the substrate. When making use of dipping, the most inexpensive method, tooling is used that serves to hold the lens while it is being manipulated and in particular while it is immersed in the treatment bath. Such holding tooling typically consists in an individual clamp having three branches engaging each lens on its edge face in three point or linear contact zones of its periphery, comprising two lateral contact zones and one bottom contact zone. In order to treat as many lenses as possible, the tooling may also consist in a “basket” capable of receiving a plurality of lenses simultaneously, and giving each of them the three above-mentioned bearing zones.
It is found that use of such tooling generates defects on the lens, which defects consist in the appearance of running and/or meniscuses of solidified varnish. Such meniscuses, in particular, consist in zones where the deposited material is too thick and they occur at the periphery at the points of contact between the lens and the tooling, penetrating radially several millimeters towards the center of the lens, thereby affecting the working portion thereof. These zones of extra thickness harm the quality of the coating, and more generally they harm the appearance and even the optical functions of the lens. Such local zones of extra thickness are particularly undesirable when depositing a thin layer that is to present uniform thickness, as applies in particular for so-called “quarter-wave” layers seeking to reduce the intensity of the optical phenomenon of interference fringes appearing at the interface between the substrate and the coating layer, and associated with them having different refractive indices.